The present invention relates to a storage device, and more particularly to a storage device which can operate suitably even when data stored in a storage area of the storage device is stored in another storage area.
Applications providing web services have undergone a fast evolution in the wake of the dramatic development in Internet technology of recent years. The volume of operational data handled by the applications themselves has also seen a rapid increase. The access frequency by the application and the utility value of such operational data change over time. There are instances where access frequency changes widely in accordance with the usage status of the web service. The reliability required from such operational data varies also depending on the type of the web service being provided. Data life cycle is defined as the series of stages from creation of such operational data, through use and storage, up to data elimination. In order for applications to be able to provide better web services with limited storage resources, operational data must be stored by selecting optimal storage in accordance with the essential requirements (usage value, performance, reliability) of the operational data of the application, at every stage of the life cycle of the operational data.
Thanks to storage network technologies developed in recent years, typified by SAN, it has become possible to centralize and mange heterogeneous and varied storage schemes in storage network environments. In addition, other large-capacity storage devices incorporating low-cost storage devices such as S-ATA have come into the market, bringing in their wake more variety as regards storage resource reliability and characteristics such as performance and the like. As a result, it has become possible to store operational data by selecting an optimal storage scheme in accordance with the essential requirements of the operational data of applications, at every stage of the life cycle of the operational data. At the same time, methods have been proposed for migrating data in accordance with data usage frequency, in which when data usage frequency in a same storage subsystem exceeds a certain threshold value, the relevant data are migrated to a high-performance volume in the same storage subsystem, and conversely, when data usage frequency in a same storage subsystem drops below a certain threshold value, the relevant data are migrated to a low-performance volume in the same storage subsystem (see, for instance, Japanese Patent Application Laid-open No. 2003-216460). Other methods have also been proposed for migrating data, in accordance with data usage, between different types of storage subsystems, in which when data usage frequency exceeds a certain threshold value, the relevant data are migrated to volumes of a high-performance storage subsystem, and conversely, when data usage frequency drops below a certain threshold value, the relevant data are migrated to volumes of a low-performance storage subsystem (see, for instance, Japanese Patent Application Laid-open No. 2005-276017).